Lithographic apparatus and device manufacturing method utilizing 2D run length encoding for image data compression

ABSTRACT

A lithographic apparatus comprises an array of individually controllable elements and a data processing pipeline. The array of individually controllable elements modulates a beam of radiation. The data processing pipeline converts a first representation of a requested dose pattern to a sequence of control data suitable for controlling the array of individually controllable elements in order substantially to form the requested dose pattern on a substrate. The data processing pipeline comprises an offline pre-processing device and an online rasterizer. The offline pre-processing device converts the first representation of the requested dose pattern to an intermediate representation, which can be rasterized in a fewer number of operations than the first representation. The storage device stores the intermediate representation. The online rasterizer accesses the stored intermediate representation and produces therefrom a stream of bitmap data to be used to generate the sequence of control data substantially in real time.

BACKGROUND

1. Field

The present invention relates to a lithographic apparatus and a methodfor manufacturing a device.

2. Related Art

A lithographic apparatus is a machine that applies a desired patternonto a substrate or part of a substrate. A lithographic apparatus can beused, for example, in the manufacture of flat panel displays, integratedcircuits (ICs) and other devices involving fine structures. In aconventional apparatus, a patterning device, which can be referred to asa mask or a reticle, can be used to generate a circuit patterncorresponding to an individual layer of a flat panel display (or otherdevice). This pattern can be transferred on (part of) the substrate(e.g., a glass plate), e.g., via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate.

Instead of a circuit pattern, the patterning means can be used togenerate other patterns, for example a color filter pattern or a matrixof dots. Instead of a mask, the patterning device can comprise apatterning array that comprises an array of individually controllableelements. The pattern can be changed more quickly and for less cost insuch a system compared to a mask-based system.

A flat panel display substrate can be rectangular in shape. Lithographicapparatus designed to expose a substrate of this type can provide anexposure region that covers a full width of the rectangular substrate,or which covers a portion of the width (for example half of the width).The substrate can be scanned underneath the exposure region, while themask or reticle is synchronously scanned through the projection beam. Inthis way, the pattern is transferred to the substrate. If the exposureregion covers the full width of the substrate then exposure can becompleted with a single scan. If the exposure region covers, forexample, half of the width of the substrate, then the substrate can bemoved transversely after the first scan, and a further scan is typicallyperformed to expose the remainder of the substrate.

The device pattern and/or corresponding radiation dose pattern can bedefined descriptively, for example in terms of vectors and/or groups ofvectors (using hierarchy, for example). The GDSII (Graphical DesignSystem II) format is in common use for defining flat panel displays, forexample, and makes use of a vector-based description with hierarchy.

Such “high-level” descriptive representations, which typically comprisea certain degree of intrinsic compression, may need to be converted tobitmap data in order to generate a control signal suitable for apatterning array. In addition, the resulting control signal needs to beprovided to the patterning array substantially in the order in whichindividual exposures are to be made, and at a suitable speed. Thisbecomes difficult for complex device patterns due to the enormous sizeof the bitmap representations and the associated difficulties concerningstorage, data conversion steps (to the bitmap data, for example) and/ortransmission, for example.

Therefore, what is needed is a system and method to more effectively usepattern data.

SUMMARY

In one embodiment, there is provided a lithographic apparatus comprisingan array of individually controllable elements and a data processingpipeline. The array of individually controllable elements modulates abeam of radiation. The data processing pipeline converts a firstrepresentation of a requested dose pattern to a sequence of control datasuitable for controlling the array of individually controllable elementsin order substantially to form the requested dose pattern on asubstrate. The data processing pipeline comprises an offlinepre-processing device and an online rasterizer. The offlinepre-processing device converts the first representation of the requesteddose pattern to an intermediate representation, which can be rasterizedin a fewer number of operations than the first representation. Thestorage device stores the intermediate representation. The onlinerasterizer accesses the stored intermediate representation and producestherefrom a stream of bitmap data to be used to generate the sequence ofcontrol data substantially in real time.

According to one embodiment of the invention, there is provided a devicemanufacturing method comprising the following steps. Using an array ofindividually controllable elements to modulate a beam of radiation.Converting a first representation of a requested dose pattern to asequence of control data suitable for controlling the array ofindividually controllable elements in order substantially to form therequested dose pattern on a substrate; converting the firstrepresentation of the requested dose pattern offline to an intermediaterepresentation that can be rasterized in a fewer number of operationsthan the first representation; storing the intermediate representationin a storage device; and accessing the stored intermediaterepresentation and producing therefrom a stream of bitmap data to beused to generate the sequence of control data substantially in realtime.

Further embodiments, features, and advantages of the present inventions,as well as the structure and operation of the various embodiments of thepresent invention, are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate one or more embodiments of the presentinvention and, together with the description, further serve to explainthe principles of the invention and to enable a person skilled in thepertinent art to make and use the invention.

FIGS. 1 and 2 depict lithographic apparatus, according to variousembodiments of the present invention.

FIG. 3 depicts a mode of transferring a pattern to a substrate using anembodiment of the invention as show in FIG. 2.

FIG. 4 depicts an arrangement of optical engines, according to oneembodiment of the present invention.

FIG. 5 depicts a data processing pipeline or “data-path,” according toone embodiment of the present invention

FIG. 6 depicts an example pattern to be defined by modification riles,according to one embodiment of the present invention

FIG. 7 illustrates an example definition of a “trapezoid” patternelement according to one embodiment of the present invention

FIG. 8 depicts an requested pattern, according to one embodiment of thepresent invention

FIG. 9 depicts the pattern of FIG. 8 represented as a plurality ofpolygons, according to one embodiment of the present invention

FIG. 10 depicts the pattern of FIG. 8 after processing to remove overlapbetween polygons, according to one embodiment of the present invention

FIG. 11 depicts the pattern of FIG. 9 after processing to decompose thepolygons into trapezoids, according to one embodiment of the presentinvention

FIG. 12 depicts how a substrate can be sliced for the purposes ofparallel rasterization, according to one embodiment of the presentinvention

FIG. 13 depicts an offline pre-processor configured to deal separatelywith display and border areas of a flat panel display pattern, accordingto one embodiment of the present invention.

FIG. 14 depicts how a pattern can be divided in a quadtreerepresentation, according to one embodiment of the present invention

FIG. 15 depicts how a multi-tree representation can be adapted tolithography machine geometry, according to one embodiment of the presentinvention.

The present invention will now be described with reference to theaccompanying drawings. In the drawings, like reference numbers mayindicate identical or functionally similar elements. Additionally, theleft-most digit(s) of a reference number may identify the drawing inwhich the reference number first appears.

DETAILED DESCRIPTION

While specific configurations and arrangements are discussed, it shouldbe understood that this is done for illustrative purposes only. A personskilled in the pertinent art will recognize that other configurationsand arrangements can be used without departing from the spirit and scopeof the present invention. It will be apparent to a person skilled in thepertinent art that this invention can also be employed in a variety ofother applications.

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises an illuminationsystem EL, a patterning device PD, a substrate table WT, and aprojection system PS. The illumination system (illuminator) IL isconfigured to condition a radiation beam B (e.g., UV radiation).

The patterning device PD (e.g., a reticle or mask or an array ofindividually controllable elements) modulates the projection beam. Ingeneral, the position of the array of individually controllable elementswill be fixed relative to the projection system PS. However, it caninstead be connected to a positioner configured to accurately positionthe array of individually controllable elements in accordance withcertain parameters.

The substrate table WT is constructed to support a substrate (e.g., aresist-coated substrate) W and connected to a positioner PW configuredto accurately position the substrate in accordance with certainparameters.

The projection system (e.g., a refractive projection lens system) PS isconfigured to project the beam of radiation modulated by the array ofindividually controllable elements onto a target portion C (e.g.,comprising one or more dies) of the substrate W.

The illumination system can include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The term “patterning device” or “contrast device” used herein should bebroadly interpreted as referring to any device that can be used tomodulate the cross-section of a radiation beam, such as to create apattern in a target portion of the substrate. The devices can be eitherstatic patterning devices (e.g., masks or reticles) or dynamic (e.g.,arrays of programmable elements) patterning devices. For brevity, mostof the description will be in terms of a dynamic patterning device,however it is to be appreciated that a static pattern device can also beused without departing from the scope of the present invention.

It should be noted that the pattern imparted to the radiation beam maynot exactly correspond to the desired pattern in the target portion ofthe substrate, for example if the pattern includes phase-shiftingfeatures or so called assist features. Similarly, the pattern eventuallygenerated on the substrate may not correspond to the pattern formed atany one instant on the array of individually controllable elements. Thiscan be the case in an arrangement in which the eventual pattern formedon each part of the substrate is built up over a given period of time ora given number of exposures during which the pattern on the array ofindividually controllable elements and/or the relative position of thesubstrate changes.

Generally, the pattern created on the target portion of the substratewill correspond to a particular functional layer in a device beingcreated in the target portion, such as an integrated circuit or a flatpanel display (e.g., a color filter layer in a flat panel display or athin film transistor layer in a flat panel display). Examples of suchpatterning devices include, e.g., reticles, programmable mirror arrays,laser diode arrays, light emitting diode arrays, grating light valves,and LCD arrays.

Patterning devices whose pattern is programmable with the aid ofelectronic means (e.g., a computer), such as patterning devicescomprising a plurality of programmable elements (e.g., all the devicesmentioned in the previous sentence except for the reticle), arecollectively referred to herein as “contrast devices.” In one example,the patterning device comprises at least 10 programmable elements, e.g.,at least 100, at least 1000, at least 10000, at least 100000, at least1000000, or at least 10000000 programmable elements.

A programmable mirror array can comprise a matrix-addressable surfacehaving a viscoelastic control layer and a reflective surface. The basicprinciple behind such an apparatus is that, e.g., addressed areas of thereflective surface reflect incident light as diffracted light, whereasunaddressed areas reflect incident light as undiffracted light. Using anappropriate spatial filter, the undiffracted light can be filtered outof the reflected beam, leaving only the diffracted light to reach thesubstrate. In this manner, the beam becomes patterned according to theaddressing pattern of the matrix-addressable surface.

It will be appreciated that, as an alternative, the filter can filterout the diffracted light, leaving the undiffracted light to reach thesubstrate.

An array of diffractive optical MEMS devices (micro-electro-mechanicalsystem devices) can also be used in a corresponding manner. In oneexample, a diffractive optical MEMS device is comprised of a pluralityof reflective ribbons that can be deformed relative to one another toform a grating that reflects incident light as diffracted light.

A further alternative example of a programmable mirror array employs amatrix arrangement of tiny mirrors, each of which can be individuallytilted about an axis by applying a suitable localized electric field, orby employing piezoelectric actuation means. Once again, the mirrors arematrix-addressable, such that addressed mirrors reflect an incomingradiation beam in a different direction to unaddressed mirrors; in thismanner, the reflected beam can be patterned according to the addressingpattern of the matrix-addressable mirrors. The required matrixaddressing can be performed using suitable electronic means.

Another example PD is a programmable LCD array.

The lithographic apparatus can comprise one or more contrast devices.For example, it can have a plurality of arrays of individuallycontrollable elements, each controlled independently of each other. Insuch an arrangement, some or all of the arrays of individuallycontrollable elements can have at least one of a common illuminationsystem (or part of an illumination system), a common support structurefor the arrays of individually controllable elements, and/or a commonprojection system (or part of the projection system).

In an example, such as the embodiment depicted in FIG. 1, the substrateW has a substantially circular shape, optionally with a notch and/or aflattened edge along part of its perimeter. In an example, the substratehas a polygonal shape, e.g., a rectangular shape.

In example where the substrate has a substantially circular shapeinclude examples where the substrate has a diameter of at least 25 mm,for instance at least 50 mm, at least 75 mm, at least 100 mm, at least125 mm, at least 150 mm, at least 175 mm, at least 200 mm, at least 250mm, or at least 300 mm. In an embodiment, the substrate has a diameterof at most 500 mm, at most 400 mm, at most 350 mm, at most 300 mm, atmost 250 mm, at most 200 mm, at most 150 mm, at most 100 mm, or at most75 mm.

In examples where the substrate is polygonal, e.g., rectangular, includeexamples where at least one side, e.g., at least 2 sides or at least 3sides, of the substrate has a length of at least 5 cm, e.g., at least 25cm, at least 50 cm, at least 100 cm, at least 150 cm, at least 200 cm,or at least 250 cm.

In one example, at least one side of the substrate has a length of atmost 1000 cm, e.g., at most 750 cm, at most 500 cm, at most 350 cm, atmost 250 cm, at most 150 cm, or at most 75 cm.

In one example, the substrate W is a wafer, for instance a semiconductorwafer. In one example, the wafer material is selected from the groupconsisting of Si, SiGe, SiGeC, SiC, Ge, GaAs, InP, and InAs. In oneexample, the wafer is a III/V compound semiconductor wafer. In oneexample, the wafer is a silicon wafer. In an embodiment, the substrateis a ceramic substrate. In one example, the substrate is a glasssubstrate. In one example, the substrate is a plastic substrate. In oneexample, the substrate is transparent (for the naked human eye). In oneexample, the substrate is colored. In one example, the substrate isabsent a color.

The thickness of the substrate can vary and, to an extent, can depend,e.g., on the substrate material and/or the substrate dimensions. In oneexample, the thickness is at least 50 μm, e.g., at least 100 μm, atleast 200 μm, at least 300 μm, at least 400 μm, at least 500 μm, or atleast 600 μm. In one example, the thickness of the substrate is at most5000 μm, e.g., at most 3500 μm, at most 2500 μm, at most 1750 μm, atmost 1250 μm, at most 1000 μm, at most 800 μm, at most 600 μm, at most500 μm, at most 400 μm, or at most 300 μm.

The substrate referred to herein can be processed, before or afterexposure, in for example a track (a tool that typically applies a layerof resist to a substrate and develops the exposed resist), a metrologytool, and/or an inspection tool. In one example, a resist layer isprovided on the substrate.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein can be considered as synonymous with the moregeneral term “projection system.”

The projection system can image the pattern on the array of individuallycontrollable elements, such that the pattern is coherently formed on thesubstrate. Alternatively, the projection system can image secondarysources for which the elements of the array of individually controllableelements act as shutters. In this respect, the projection system cancomprise an array of focusing elements such as a micro lens array (knownas an MLA) or a Fresnel lens array, e.g., to form the secondary sourcesand to image spots onto the substrate. In one example, the array offocusing elements (e.g., MLA) comprises at least 10 focus elements,e.g., at least 100 focus elements, at least 1000 focus elements, atleast 10000 focus elements, at least 100000 focus elements, or at least1000000 focus elements. In one example, the number of individuallycontrollable elements in the patterning device is equal to or greaterthan the number of focusing elements in the array of focusing elements.In one example, one or more (e.g., 1000 or more, the majority, or abouteach) of the focusing elements in the array of focusing elements can beoptically associated with one or more of the individually controllableelements in the array of individually controllable elements, e.g., with2 or more of the individually controllable elements in the array ofindividually controllable elements, such as 3 or more, 5 or more, 10 ormore, 20 or more, 25 or more, 35 or more, or 50 or more. In one example,the MLA is movable (e.g., with the use of actuators) at least in thedirection to and away from the substrate, e.g., with the use of one ormore actuators. Being able to move the MLA to and away from thesubstrate allows, e.g., for focus adjustment without having to move thesubstrate.

As herein depicted in FIGS. 1 and 2, the apparatus is of a reflectivetype (e.g., employing a reflective array of individually controllableelements). Alternatively, the apparatus can be of a transmissive type(e.g., employing a transmissive array of individually controllableelements).

The lithographic apparatus can be of a type having two (dual stage) ormore substrate tables. In such “multiple stage” machines, the additionaltables can be used in parallel, or preparatory steps can be carried outon one or more tables while one or more other tables are being used forexposure.

The lithographic apparatus can also be of a type wherein at least aportion of the substrate can be covered by an “immersion liquid” havinga relatively high refractive index, e.g., water, so as to fill a spacebetween the projection system and the substrate. An immersion liquid canalso be applied to other spaces in the lithographic apparatus, forexample, between the patterning device and the projection system.Immersion techniques are well known in the art for increasing thenumerical aperture of projection systems. The term “immersion” as usedherein does not mean that a structure, such as a substrate, must besubmerged in liquid, but rather only means that liquid is locatedbetween the projection system and the substrate during exposure.

Referring again to FIG. 1, the illuminator IL receives a radiation beamfrom a radiation source SO. In one example, the radiation sourceprovides radiation having a wavelength of at least 5 nm, e.g., at least10 nm, at least 5 nm, at least 100 nm, at least 150 nm, at least 175 nm,at least 200 nm, at least 250 nm, at least 275 nm, at least 300 nm, atleast 325 nm, at least 350 nm, or at least 360 nm. In one example, theradiation provided by radiation source SO has a wavelength of at most450 nm, e.g., at most 425 nm, at most 375 nm, at most 360 nm, at most325 nm, at most 275 nm, at most 250 nm, at most 225 nm, at most 200 nm,or at most 175 nm. In one example, the radiation has a wavelengthincluding 436 nm, 405 nm, 365 nm, 355 nm, 248 nm, 193 nm, 157 nm, and/or126 nm. In one example, the radiation includes a wavelength of around365 nm or around 355 nm. In one example, the radiation includes a broadband of wavelengths, for example encompassing 365, 405, and 436 nm. A355 nm laser source could be used. The source and the lithographicapparatus can be separate entities, for example when the source is anexcimer laser. In such cases, the source is not considered to form partof the lithographic apparatus and the radiation beam is passed from thesource SO to the illuminator IL with the aid of a beam delivery systemBD comprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source can be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, can be referred to as a radiation system.

The illuminator IL, can comprise an adjuster AD for adjusting theangular intensity distribution of the radiation beam. Generally, atleast the outer and/or inner radial extent (commonly referred to asσ-outer and σ-inner, respectively) of the intensity distribution in apupil plane of the illuminator can be adjusted. In addition, theilluminator IL can comprise various other components, such as anintegrator IN and a condenser CO. The illuminator can be used tocondition the radiation beam to have a desired uniformity and intensitydistribution in its cross-section. The illuminator IL, or an additionalcomponent associated with it, can also be arranged to divide theradiation beam into a plurality of sub-beams that can, for example, eachbe associated with one or a plurality of the individually controllableelements of the array of individually controllable elements. Atwo-dimensional diffraction grating can, for example, be used to dividethe radiation beam into sub-beams. In the present description, the terms“beam of radiation” and “radiation beam” encompass, but are not limitedto, the situation in which the beam is comprised of a plurality of suchsub-beams of radiation.

The radiation beam B is incident on the patterning device PD (e.g., anarray of individually controllable elements) and is modulated by thepatterning device. Having been reflected by the patterning device PD,the radiation beam B passes through the projection system PS, whichfocuses the beam onto a target portion C of the substrate W. With theaid of the positioner PW and position sensor IF2 (e.g., aninterferometric device, linear encoder, capacitive sensor, or the like),the substrate table WT can be moved accurately, e.g., so as to positiondifferent target portions C in the path of the radiation beam B. Whereused, the positioning means for the array of individually controllableelements can be used to correct accurately the position of thepatterning device PD with respect to the path of the beam B, e.g.,during a scan.

In one example, movement of the substrate table WT is realized with theaid of a long-stroke module (course positioning) and a short-strokemodule (fine positioning), which are not explicitly depicted in FIG. 1.In one example, the apparatus is absent at least a short stroke modulefor moving substrate table WT. A similar system can also be used toposition the array of individually controllable elements. It will beappreciated that the projection beam B can alternatively/additionally bemoveable, while the object table and/or the array of individuallycontrollable elements can have a fixed position to provide the requiredrelative movement. Such an arrangement can assist in limiting the sizeof the apparatus. As a further alternative, which can, e.g., beapplicable in the manufacture of flat panel displays, the position ofthe substrate table WT and the projection system PS can be fixed and thesubstrate W can be arranged to be moved relative to the substrate tableWT. For example, the substrate table WT can be provided with a systemfor scanning the substrate W across it at a substantially constantvelocity.

As shown in FIG. 1, the beam of radiation B can be directed to thepatterning device PD by means of a beam splitter BS configured such thatthe radiation is initially reflected by the beam splitter and directedto the patterning device PD. It should be realized that the beam ofradiation B can also be directed at the patterning device without theuse of a beam splitter. In one example, the beam of radiation isdirected at the patterning device at an angle between 0 and 90°, e.g.,between 5 and 85°, between 15 and 75°, between 25 and 65°, or between 35and 55° (the embodiment shown in FIG. 1 is at a 90° angle). Thepatterning device PD modulates the beam of radiation B and reflects itback to the beam splitter BS which transmits the modulated beam to theprojection system PS. It will be appreciated, however, that alternativearrangements can be used to direct the beam of radiation B to thepatterning device PD and subsequently to the projection system PS. Inparticular, an arrangement such as is shown in FIG. 1 may not berequired if a transmissive patterning device is used.

The depicted apparatus can be used in several modes:

1. In step mode, the array of individually controllable elements and thesubstrate are kept essentially stationary, while an entire patternimparted to the radiation beam is projected onto a target portion C atone go (i.e., a single static exposure). The substrate table WT is thenshifted in the X and/or Y direction so that a different target portion Ccan be exposed. In step mode, the maximum size of the exposure fieldlimits the size of the target portion C imaged in a single staticexposure.

2. In scan mode, the array of individually controllable elements and thesubstrate are scanned synchronously while a pattern imparted to theradiation beam is projected onto a target portion C (i.e., a singledynamic exposure). The velocity and direction of the substrate relativeto the array of individually controllable elements can be determined bythe (de-) magnification and image reversal characteristics of theprojection system PS. In scan mode, the maximum size of the exposurefield limits the width (in the non-scanning direction) of the targetportion in a single dynamic exposure, whereas the length of the scanningmotion determines the height (in the scanning direction) of the targetportion.

3. In pulse mode, the array of individually controllable elements iskept essentially stationary and the entire pattern is projected onto atarget portion C of the substrate W using a pulsed radiation source. Thesubstrate table WT is moved with an essentially constant speed such thatthe projection beam B is caused to scan a line across the substrate W.The pattern on the array of individually controllable elements isupdated as required between pulses of the radiation system and thepulses are timed such that successive target portions C are exposed atthe required locations on the substrate W. Consequently, the projectionbeam B can scan across the substrate W to expose the complete patternfor a strip of the substrate. The process is repeated until the completesubstrate W has been exposed line by line.

4. In continuous scan mode, essentially the same as pulse mode exceptthat the substrate W is scanned relative to the modulated beam ofradiation B at a substantially constant speed and the pattern on thearray of individually controllable elements is updated as the projectionbeam B scans across the substrate W and exposes it. A substantiallyconstant radiation source or a pulsed radiation source, synchronized tothe updating of the pattern on the array of individually controllableelements, can be used.

5. In pixel grid imaging mode, which can be performed using thelithographic apparatus of FIG. 2, the pattern formed on substrate W isrealized by subsequent exposure of spots formed by a spot generator thatare directed onto patterning device PD. The exposed spots havesubstantially the same shape. On substrate W the spots are printed insubstantially a grid. In one example, the spot size is larger than apitch of a printed pixel grid, but much smaller than the exposure spotgrid. By varying intensity of the spots printed, a pattern is realized.In between the exposure flashes the intensity distribution over thespots is varied.

Combinations and/or variations on the above described modes of use orentirely different modes of use can also be employed.

In lithography, a pattern is exposed on a layer of resist on thesubstrate. The resist is then developed. Subsequently, additionalprocessing steps are performed on the substrate. The effect of thesesubsequent processing steps on each portion of the substrate depends onthe exposure of the resist. In particular, the processes are tuned suchthat portions of the substrate that receive a radiation dose above agiven dose threshold respond differently to portions of the substratethat receive a radiation dose below the dose threshold. For example, inan etching process, areas of the substrate that receive a radiation doseabove the threshold are protected from etching by a layer of developedresist. However, in the post-exposure development, the portions of theresist that receive a radiation dose below the threshold are removed andtherefore those areas are not protected from etching. Accordingly, adesired pattern can be etched. In particular, the individuallycontrollable elements in the patterning device are set such that theradiation that is transmitted to an area on the substrate within apattern feature is at a sufficiently high intensity that the areareceives a dose of radiation above the dose threshold during theexposure. The remaining areas on the substrate receive a radiation dosebelow the dose threshold by setting the corresponding individuallycontrollable elements to provide a zero or significantly lower radiationintensity.

In practice, the radiation dose at the edges of a pattern feature doesnot abruptly change from a given maximum dose to zero dose even if theindividually controllable elements are set to provide the maximumradiation intensity on one side of the feature boundary and the minimumradiation intensity on the other side. Instead, due to diffractiveeffects, the level of the radiation dose drops off across a transitionzone. The position of the boundary of the pattern feature ultimatelyformed by the developed resist is determined by the position at whichthe received dose drops below the radiation dose threshold. The profileof the drop-off of radiation dose across the transition zone, and hencethe precise position of the pattern feature boundary, can be controlledmore precisely by setting the individually controllable elements thatprovide radiation to points on the substrate that are on or near thepattern feature boundary not only to maximum or minimum intensity levelsbut also to intensity levels between the maximum and minimum intensitylevels. This is commonly referred to as “grayscaling.”

Grayscaling provides greater control of the position of the patternfeature boundaries than is possible in a lithography system in which theradiation intensity provided to the substrate by a given individuallycontrollable element can only be set to two values (namely just amaximum value and a minimum value). In an embodiment, at least threedifferent radiation intensity values can be projected onto thesubstrate, e.g., at least 4 radiation intensity values, at least 8radiation intensity values, at least 16 radiation intensity values, atleast 32 radiation intensity values, at least 64 radiation intensityvalues, at least 128 radiation intensity values, or at least 256radiation intensity values.

It should be appreciated that grayscaling can be used for additional oralternative purposes to that described above. For example, theprocessing of the substrate after the exposure can be tuned, such thatthere are more than two potential responses of regions of the substrate,dependent on received radiation dose level. For example, a portion ofthe substrate receiving a radiation dose below a first thresholdresponds in a first manner; a portion of the substrate receiving aradiation dose above the first threshold but below a second thresholdresponds in a second manner; and a portion of the substrate receiving aradiation dose above the second threshold responds in a third manner.Accordingly, grayscaling can be used to provide a radiation dose profileacross the substrate having more than two desired dose levels. In anembodiment, the radiation dose profile has at least 2 desired doselevels, e.g., at least 3 desired radiation dose levels, at least 4desired radiation dose levels, at least 6 desired radiation dose levelsor at least 8 desired radiation dose levels.

It should further be appreciated that the radiation dose profile can becontrolled by methods other than by merely controlling the intensity ofthe radiation received at each point on the substrate, as describedabove. For example, the radiation dose received by each point on thesubstrate can alternatively or additionally be controlled by controllingthe duration of the exposure of the point. As a further example, eachpoint on the substrate can potentially receive radiation in a pluralityof successive exposures. The radiation dose received by each point can,therefore, be alternatively or additionally controlled by exposing thepoint using a selected subset of the plurality of successive exposures.

In order to form the required pattern on the substrate, it is necessaryto set each of the individually controllable elements in the patterningdevice to the requisite state at each stage during the exposure process.Therefore, control signals, representing the requisite states, must betransmitted to each of the individually controllable elements. In oneexample, the lithographic apparatus includes a controller that generatesthe control signals. The pattern to be formed on the substrate can beprovided to the lithographic apparatus in a vector-defined format, suchas GDSII. In order to convert the design information into the controlsignals for each individually controllable element, the controllerincludes one or more data manipulation devices, each configured toperform a processing step on a data stream that represents the pattern.The data manipulation devices can collectively be referred to as the“datapath.”

The data manipulation devices of the datapath can be configured toperform one or more of the following functions: converting vector-baseddesign information into bitmap pattern data; converting bitmap patterndata into a required radiation dose map (namely a required radiationdose profile across the substrate); converting a required radiation dosemap into required radiation intensity values for each individuallycontrollable element; and converting the required radiation intensityvalues for each individually controllable element into correspondingcontrol signals.

FIG. 2 depicts an arrangement of the apparatus according to the presentinvention that can be used, e.g., in the manufacture of flat paneldisplays. Components corresponding to those shown in FIG. 1 are depictedwith the same reference numerals. Also, the above descriptions of thevarious embodiments, e.g., the various configurations of the substrate,the contrast device, the MLA, the beam of radiation, etc., remainapplicable.

FIG. 2 depicts an arrangement of a lithographic apparatus, according toone embodiment of the present invention. This embodiment can be used,e.g., in the manufacture of flat panel displays. Componentscorresponding to those shown in FIG. 1 are depicted with the samereference numerals. Also, the above descriptions of the variousembodiments, e.g., the various configurations of the substrate, thecontrast device, the MLA, the beam of radiation, etc., remainapplicable.

As shown in FIG. 2, the projection system PS includes a beam expander,which comprises two lenses L1, L2. The first lens L1 is arranged toreceive the modulated radiation beam B and focus it through an aperturein an aperture stop AS. A further lens AL can be located in theaperture. The radiation beam B then diverges and is focused by thesecond lens L2 (e.g., a field lens).

The projection system PS further comprises an array of lenses MLAarranged to receive the expanded modulated radiation B. Differentportions of the modulated radiation beam B, corresponding to one or moreof the individually controllable elements in the patterning device PD,pass through respective different lenses in the array of lenses MLA.Each lens focuses the respective portion of the modulated radiation beamB to a point which lies on the substrate W. In this way an array ofradiation spots S is exposed onto the substrate W. It will beappreciated that, although only eight lenses of the illustrated array oflenses 14 are shown, the array of lenses can comprise many thousands oflenses (the same is true of the array of individually controllableelements used as the patterning device PD).

FIG. 3 illustrates schematically how a pattern on a substrate W isgenerated using the system of FIG. 2, according to one embodiment of thepresent invention. The filled in circles represent the array of spots Sprojected onto the substrate W by the array of lenses MLA in theprojection system PS. The substrate W is moved relative to theprojection system PS in the Y direction as a series of exposures areexposed on the substrate W. The open circles represent spot exposures SEthat have previously been exposed on the substrate W. As shown, eachspot projected onto the substrate by the array of lenses within theprojection system PS exposes a row R of spot exposures on the substrateW. The complete pattern for the substrate is generated by the sum of allthe rows R of spot exposures SE exposed by each of the spots S. Such anarrangement is commonly referred to as “pixel grid imaging,” discussedabove.

It can be seen that the array of radiation spots S is arranged at anangle θ relative to the substrate W (the edges of the substrate lieparallel to the X and Y directions). This is done so that when thesubstrate is moved in the scanning direction (the Y-direction), eachradiation spot will pass over a different area of the substrate, therebyallowing the entire substrate to be covered by the array of radiationspots 15. In one example, the angle θ is at most 20°, 10°, e.g., at most5°, at most 3°, at most 1°, at most 0.5°, at most 0.25°, at most 0.10°,at most 0.05°, or at most 0.01°. In one example, the angle θ is at least0.001°.

FIG. 4 shows schematically how an entire flat panel display substrate Wcan be exposed in a single scan using a plurality of optical engines,according to one embodiment of the present invention. In the exampleshown eight arrays 31 of radiation spots S are produced by eight opticalengines (not shown), arranged in two rows 32,33 in a ‘chess board’configuration, such that the edge of one array of radiation spots Sslightly overlaps (in the scanning direction Y) with the edge of theadjacent array of radiation spots 15. In one example, the opticalengines are arranged in at least 3 rows, for instance 4 rows or 5 rows.In this way, a band of radiation extends across the width of thesubstrate W, allowing exposure of the entire substrate to be performedin a single scan. It will be appreciated that any suitable number ofoptical engines can be used. In one example, the number of opticalengines is at least 1, e.g., at least 2, at least 4, at least 8, atleast 10, at least 12, at least 14, or at least 17. In one example, thenumber of optical engines is less than 40, e.g., less than 30 or lessthan 20.

Each optical engine can comprise a separate illumination system IL,patterning device PD and projection system PS as described above. It isto be appreciated, however, that two or more optical engines can shareat least a part of one or more of the illumination system, patterningdevice and projection system.

A device pattern and/or corresponding radiation dose pattern to beexposed on the substrate can be designed in a vector-based designpackage to produce a representation of the requested design in avector-based file format such as “GDSII”. The resulting pattern can bestored as a “descriptive representation.” Where a vector-based designpackage is used, for example, the descriptive representation can storethe layout of device features in terms of individual vectors describingfeature contours. Additionally or alternatively, the descriptiverepresentation can incorporate curves or other basic elementsappropriate to the device being described.

Practical devices are often built up from repeating units of differenttypes. Each of these repeating units can, in turn, be built up from avariety of repeating sub-units, etc. This repetition can be dealt within the descriptive representation by means of a hierarchy ortree-structure, which ensures that each repeating unit only has to bedescribed once (or, at least, does not have to be explicitly re-definedfor each instance in the pattern). Higher-level units in the hierarchycan be defined, where appropriate, in terms of references to otherrepeating units defined once elsewhere.

Hierarchical representation is efficient in that it allows a complexrepeating device pattern to be stored as a relatively small file.However, this kind of representation is not suitable for controlling thearray of individually controllable elements that is to produce thepattern on the substrate. As described above, the pattern produced onthe substrate by the array of individually controllable elements isbuilt up over time by a grid of radiation spots scanned over the surfaceof the substrate, the intensity associated with each being controlled byparticular elements of the array of individually controllable elementsat particular times. The control signal that is sent to the array ofindividually controllable elements is therefore derived from a bitmaprepresentation of the pattern.

A conversion is therefore necessary between the non-bitmap descriptiverepresentation of the requested dose pattern and the bitmap version ofthis data that forms the basis of the control signal forwardedeventually to the patterning device. The control signal cannot normallycomprise hierarchy and needs to describe each repeating featureexplicitly. This leads to a dramatic increase in the volume of patterndata relative to the descriptive representation.

As an example, a flat panel display can be built up from pixels of300×300 microns on a substrate of 2.6×2.8 meters. Each pixel isidentical and has a sub-structure that can be defined in terms of 3750corner points or vertices. This means that the patterned substrate willhave 300 billion vertices associated with the display pixel pattern,which, allocating 8 bytes for each vertex, results in a pattern file inexcess of 2 terabytes when no hierarchy is present (and not takingaccount of the pattern associated with the borders between displaypixels).

These enormous file sizes mean that substantial processing power andhigh capacity buffer memory facilities are required to perform theoffline processing of rasterizing the pattern data andcompressing/storing the resulting bitmap data at reasonable expense andwith minimum time delay. The need to be able to compress the rasterizeddata efficiently can also place unwanted restraints on the type ofpatterns that can be printed (e.g., a minimum level of order or maximumpattern entropy can be imposed).

According to one embodiment of the present invention, an approach isused based on a special intermediate representation of the pattern thatcan be stored efficiently and rasterized online. The arrangement isshown schematically in FIG. 5, which depicts the “data processingpipeline” or “data-path” that links the requested pattern input device500 and the patterning device PD. The data-path comprises an offlinepart, left of broken line 570, which comprises components that operatebefore exposure of the substrate begins, and an online part, right ofbroken line 570, which comprises components that operate substantiallyat that same time as the substrate is actually exposed. Links betweenindividual elements are depicted as arrows to indicate the direction ofdata flow. However, these continuous lines do not necessarily mean adirect data connection and further data processing devices can bearranged to operate between one or more of those shown.

According to this embodiment, a user defines the requested pattern viainput device 500, which is stored as a non-bitmap descriptiverepresentation in memory buffer 510. An offline pre-processor 520 thenconverts the non-bitmap descriptive representation into an intermediaterepresentation that is suitable for rasterization substantially inreal-time. The intermediate representation can be intrinsicallycompressed in comparison to the pure bitmap equivalent, so as to be moreeasily stored and extracted, but comprise data that is ordered in such away that it can more easily be rasterized than the pure non-bitmapdescriptive representation initially output from the input device 500(for example, a GDSII file). For example, rasterization can be achievedusing fewer computational operations. In particular, the intermediaterepresentation can provide the possibility of reducing the total amountof memory that is needed for rasterization as well as the total numberof memory access operations. It can also be used to limit theirregularity in the order and size of memory accesses. In particular,the intermediate representation can order data in such a way thatconsecutive memory accesses during rasterization are made as much aspossible in consecutive memory blocks. These properties of theintermediate representation help to make rasterization possible in realtime because they dictate the extent to which the rasterization can beimplemented using internal memory in dedicated rasterization hardware(e.g., SRAM memory provided within hardware based on Field ProgrammableGates Arrays (FPGAs)). Such internal memory can generally be accessedmuch more quickly than external memory but is limited in size. Inaddition, the intermediate representation can be arranged so that it canbe rasterized without any division operations. Division operations areparticular intensive in terms of the amount of memory hardware/resourcesrequired, so that creating an intermediate representation that can berasterized without such operations greatly increases the efficiency ofrasterization. The initial GDSII or vector-based representation (the“first representation”) cannot normally be rasterized without divisionsteps.

The intermediate representation of the requested pattern is passed toand stored in the online pattern memory buffer 530. The buffer 530 canbe accessible by an online pre-processor 540, which can make finaladjustments (such as a final level of decompression) to the data beforeit is passed to an online rasterizer 550, which represents the hardwarethat is configured to perform the rasterization algorithm itself. Therasterizer 550 is configured to supply bitmap data (or at least aneasily decompressed representation of bitmap data, such as aline-by-line ID run-length encoded representation) to the rest of thedata-path at a pattern transfer rate that is substantially commensuratewith the rate at which the patterning device needs to receive patterndata during exposure. An online buffer 560 can be provided to allow (andcorrect) for variations in the rasterization speed of the onlinerasterizer 550.

In one example, the above arrangement circumvents the need forvoluminous offline data compression calculations and storage means fordealing with the rasterized bitmap data because it no longer needs to bestored as a complete set. In fact, because the bitmap data is producedsubstantially in real time, only a very small fraction of the data needever be stored at any one time.

Hierarchical data representations are intrinsically more difficult torasterize because the data relating to a particular portion of thepattern can be distributed unpredictably in the design file in question.This lack of ordering reduces the efficiency with which the relevantdata can be accessed by the rasterizing hardware, which can have aparticularly damaging effect on the processing speed where the hardwareis of a massively parallel type.

According to one embodiment of the invention, the offline pre-processor520 is configured to remove one or more levels of hierarchy from thenon-bitmap descriptive representation of the pattern. Features describedin the resulting intermediate representation can then be re-ordered insuch a way as to be more efficiently accessed by the online rasterizer550.

In flat-panel displays, the element that is likely to be repeated mostoften is the display pixel itself. Therefore, it can be desirable forthe offline pre-processor 520 to remove all levels of hierarchy exceptthat of the display pixel and provide an online pre-processor 540 thatis configured to remove this last level of hierarchy online. Thisarrangement will vastly reduce the amount of the data that needs to bestored in the pattern memory buffer 530 at the expense of having toprovide additional online hardware for the online pre-processor 540.Depending on the hierarchy present in a particular pattern and therelative costs of providing extra capacity to the pattern buffer memory530 and online pre-processor 540, the offline pre-processor 520 can bearranged to provide an intermediate representation with more or fewerlevels of hierarchy.

In one example, where all levels of hierarchy are removed except thatcorresponding to individual display pixels, this can mean that thedisplay area of the flat panel display is treated differently from theborder areas, where the pattern does not comprise repeating displaypixels. In particular, the offline pre-processor 520 can be arranged toremove all hierarchy from the non-bitmap representation of the borderareas while removing all but a final level of hierarchy for the displayarea (the final level of hierarchy being that which takes account ofdisplay pixel repetition). Alternatively, where hierarchy/repetition isfound in the border areas, the offline pre-processor 520 can be arrangedto remove all but a final level of hierarchy for the border areas also,this final level corresponding to the repeating elements found in theborder areas. Where the non-bitmap descriptive representation containsonly a single level of hierarchy, the offline processor 520 can producean intermediate representation which also has only a single level ofhierarchy.

According to one embodiment of the invention, the intermediaterepresentation is a compressed representation. For example, contourfeatures can be defined in terms of vectors rather than individualpixels, the vector representation allowing groups of pixels that have aparticular relationship to each other (i.e., they lie on the same line)to be expressed in a compact form. This kind of compressedrepresentation can be seen as an extension of one-dimensional run-lengthencoding to two dimensions.

Vectors can be convenient because they are easily extracted from theuser input descriptive representation of the requested pattern(particularly where the format is vector-based, such as GDSII). Inaddition, lithography patterns are commonly constructed predominantlyfrom straight line elements, which means that they can be efficientlyexpressed in this way (unlike typical patterns in other image-processingscenarios, such as computer graphics or digital photographs).

The compressed pattern can be expressed in terms of vectors described byreference to a start point, an angle relative to an axis in the plane ofthe substrate (the scanning direction, for example), and a singlecoordinate of an end point. The constancy of the vector angle over anumber of scan lines provides the repetition that is at the root of therun-length encoding. Other forms of repetition can also be exploited.For example, any mathematical relationship (which can be expressed as ageneral algebraic equation, a polynomial expansion, or in terms ofconstant 2nd or 3rd derivatives, for example) that links a significantnumber of pixels can be used as a basis for two-dimensional run-lengthencoding of this type.

In one example, in order for the intermediate representation to berasterizable in real time, the pattern data needs to be made availableto the online rasterizer 550 substantially in the order in which thecorresponding bitmap values are to be produced so that the informationcan be accessed efficiently. More particularly, where the intermediaterepresentation comprises vectors, these vectors need to be ordered in anappropriate way by the offline pre-processor 520 so that they can beefficiently accessed by the online rasterizer 550. Where the bitmapscanning order is from left-to-right (−X to +X) and top-to-bottom (+Y to−Y), Y corresponding to the scanning direction of the substrate relativeto the patterning array, for example, and vectors are described in termsof the X and Y coordinates of their upper end, their angle, and theY-coordinate of their lower end-point, the vectors can be advantageouslyordered from top-to-bottom and from left-to-right in the intermediaterepresentation file. The left-to-right aspect of the ordering can onlybe relevant where the vector is parallel to the X axis, in which casethe end point that will be exposed first will be taken as the “upperend”, or origin of the vector. In general, the top-to-bottom orderingtakes priority as this defines which portion of the vector willcontribute first.

The above discussion is based, for simplicity, in the “dense” bitmapdomain. In an example using pixel grid imaging, the actual exposureorder does not exactly follow the line-by-line scanning order of thebitmap pattern. Neighboring points in the bitmap pattern can be exposedat slightly different times. However, once the bitmap data has beenproduced by the online rasterizer 550, it can be re-ordered relativelyeasily to form the control signal for the patterning array withoutdeparting from the scope of the invention. Similarly, straightforwardadjustments to the rasterization process itself can be made so as toproduce pixel values substantially in the order in which they will beneeded for the exposure.

In one example, the vectors (or other geometric unit representing aportion of the pattern with constant mathematical properties) can beused to establish “modification rules” for the pattern, which define foreach line of bitmap values (e.g., corresponding to a line of constant Yin the requested dose) how they are different from the bitmap values ofa preceding line. Where the pattern is expressed in terms of vectors,these modification rules will be defined by the vectors that will crossthe line in question and will need to be updated whenever a lineincludes a new vector portion or when a previously applicable vectorportion no longer crosses the line in question (i.e., it ended in thepreceding line).

According to one embodiment of the invention, the modification rulesthemselves are stored as two numbers: an X-position, and a step in X fora fixed change in Y (i.e., the description of the angle in amathematical line equation x=ay+b, and the same description as the“angle” referred to in the intermediate representation.

The intermediate representation can be expressed, for example, as astream of data packets representing modification rule updates on aline-by-line basis (i.e., the modification rule update for a given linecan define how the group of modification rules that are relevant forthat line will be different from the group of modification rules thatwere relevant for the preceding line). This representation is compressedbecause only changes (updates) to the modification rules need berecorded in each data packet. These changes will represent a smalleramount of data than the corresponding lines of bitmap values (and eventhe corresponding list of relevant modification rules) due to the vector(or at least geometrically constant) nature of the data represented bythe modification rules, which reduces the number of changes that will berequired for each line. The order of these data packets shouldcorrespond substantially to the order in which the lines of dose patterncorresponding to the lines of bitmap values will be rasterized (which isclosely related to the order in which they will be exposed). Thisprovides the advantage that the data can be accessed and rasterizedefficiently as discussed above. The hardware in the online rasterizer550 can be based on an FPGA architecture and can be configured directlyto convert this stream of modification rule updates to a bitmap patternsuitable for being used to form the control signal for the patterningarray.

In the above example(s), modification rules have been described asdefining how bitmap values change from line to line. It should beunderstood, however, that in practice the modification rules can definehow a representation of the bitmap values changes from line to line.This representation can be compressed, for example using ID run-lengthencoding. This is likely to lead to a large reduction in the data volumeleaving the rasterizer and should be straightforward to decode inreal-time. The ID run-length encoding option is likely to beparticularly efficient and easy to implement where bitmap values arerestricted to being either black or white. However, a more complexrepresentation can be required in order to cope with gray scalepatterns. Here, the bitmap values are liable to change more continuouslyalong a line of dose pattern. 1-D compression of this type of data mightbe carried out by exploiting constant properties of the bitmap valuetransitions. For example, it can be that bitmap values change at aconstant rate with respect to the X direction, in which case a gradualtransition can efficiently be represented by means of a starting pixel(defined as a position along X), a rate of change of bitmap value alongX, and an end pixel (again defined as a position along X).

Representations of vectors, angles, modification rules and modificationrules updates other than those referred to above can also be usedwithout departing from the scope of the invention.

Alternatively or additionally, the vectors can be ordered in theintermediate representation by reference to the coordinates of theirupper left end (i.e., the part of the vector that will be exposed ontothe substrate first) only, so that those with the highest Y coordinatecan be accessed earlier than those with a lower Y coordinate (asmentioned above, this is true in the “dense” or bitmap domain, but thesituation will be more complex in the pixel grid imaging domain becausethe order of exposure of pixels is not a simple function of X and Y).The modification rule updates that add modification rules describe wherevectors begin and in what direction they are going. They do not sayanything about their length/end-point. This is handled by separatemodification rule updates that remove modification rules. Or, in otherwords, the end of a vector is reached when a modification rule update isfound for the current Y position that removes the modification ruledealing with the vector in question. The algorithm responsible forrasterizing the intermediate representation will parse the file frombeginning to end, which, as mentioned above, will contain modificationrule updates arranged in order of increasing Y. Therefore, the algorithmwill begin with Y=0 and will increase Y the first, should be an additionof a modification rule pair). The modification rules will then beexecuted and Y incremented until Y reaches the value of the nextmodification rule update in the file. Note that this second modificationrule update can have the same Y value as the first one. This processwill continue until Y reaches the maximum value (i.e., the end of thesubstrate).

FIG. 6 illustrates how a shape 600 can be described in terms ofmodification rules and modification rule updates, according to oneembodiment of the present invention. The shape 600 is built up over 25scan lines (labeled Y=0 to Y=24) perpendicular to the scanning directionY. Its outline is defined by contour segments 630 within which thebitmap pixel values are set to black and outside of which the bitmapvalues are set to white. As has been described above, the intermediaterepresentation can comprise modification rule updates, which describehow the modification rules change from line to line and are ordered inthe intermediate representation in the sequence in which they are neededfor rasterization. In the example shown, the first modification ruleupdates will be found by the rasterization algorithm at line Y=0 andwill consist of the introduction of a transition pair, corresponding tothe contour outlines starting from points 602 and 604. The pair ofmodification rules introduced describe the position of the startingpoints 602 and 604 and also the angle at which the respective contoursdescend towards points 606 and 608. Both these modification rules willremain valid until the algorithm reaches Y=10 at which point one of themodification rules will need to be changed to reflect the change inangle of the left contour at point 606. This is represented by a singlemodification rule describing the change in angle. The next twomodification rule updates will be of the same type and are encounteredat Y=14 (point 608) and Y=16 (point 610). The update on line Y=20represents a shift along X so that the starting position and angle willneed to be redefined by the modification rule update. Finally, at pointY=24, the modification rule update will define the removal of amodification rule pair, corresponding to the end of the vectorsrespectively linking points 614 and 616, and 608 and 618.

For patterns of this type, the modification rules updates can be splitinto at least four generic types: (1) the addition of a pair ofmodification rules (the first member of the pair describing the start ofa feature to be represented in a particular line of bitmap values andthe second member of the pair describing the end of the feature, andthereby the thickness of the feature where it crosses the line; (2) theremoval of a pair of modification rules (when a feature ends—it isassumed that the feature has a finite thickness before ending so that apair of modification rules, rather than a single modification rule, wereneeded in the previous line); (3) a change of angle of a modificationrule (representing a change in angle of one side of the contour beingdescribed by the modification rule); and (4) a change in theX-coordinate of a modification rule (representing a ledge-type shape inone side of the contour being described by the modification rule).

The two-dimensional run-length encoding can be applied not only to dosepatterns defined by a black and white pixels, but also to those definedby gray-scale bitmap patterns (i.e., bitmaps with one or more valuesbetween those used for black and white). Such patterns can berepresented in the intermediate representation as contours that aredefined relative to sub-grid positions in the bitmap pixel grid. Forexample, a contour passing through a bitmap pixel at a height of ⅝ ofthe pixel can be rasterized as a pixel with a “gray” value of ⅝ (where 0is black and 1 is white) or some other appropriate “gray” value that isassociated with the value of ⅝.

FIG. 7 illustrates a trapezoidal approach, according to one embodimentof the present invention. This is an alternative (or in addition) to thespecial two-dimensional run-length encoded format described above, inwhich a trapezoid representation (a limited polygon representation) canbe used (“trapezoid” is here understood to mean a quadrilateral with twoparallel sides). Here, the requested pattern is decomposed intotrapezoids can be expressed in terms of an origin (X,Y) 750, height 710,width 720, first gradient dX/dY 730, and second gradient dX/dY 740.Other representations can also be used. As before, individual features(or parts of features) can advantageously be re-ordered in theintermediate representation for the purposes of efficient rasterization.For example, they can be re-ordered by reference to their origins 750and the sequence in which each origin will be exposed/rasterized.However, implementation constraints can impose other orderings.

In one example, the GDSU data can be expressed in terms of any set ofbasic shapes (“rasterization primitives”) that reduces the complexity ofthe hardware required to implement the online rasterizer 550. 2Drun-length encoding and trapezoids have been mentioned above, but otherprimitives can include triangles, rectangles or other polygons ofrestricted complexity. Whichever primitives are chosen, the offlinepre-processor 520 performs the operation of breaking pattern shapes downinto the primitives.

In one example, the simplest primitives for the rasterizer would berectangles because the rasterization algorithm normally converts thepolygons of the pattern into pixels values that are on an orthogonalpixel grid. However, a rectangles can lead to large amounts of memorybeing required for storage of non-orthogonal shapes. The trapezoid is amore efficient primitive in this respect, defined only with two opposingsides that follow pixel reference axes (X and/or Y). To handle thisprimitive, the rasterization engine can fill pixels, following scanlines: starting from one slanted line, filling up the area until thenext slanted line is reached and repeating this process line by lineuntil the trapezoid is done.

FIGS. 8 to 11 illustrate how an example pattern can be processed by theoffline pre-processor 520, according to one embodiment of the presentinvention. FIG. 8 illustrates the example pattern as designed by a user.FIG. 9 shows how this pattern can be built up from polygons in thedescriptive (GDSII) representation. These are processed in a first stageto remove the overlap and produce the pattern shown in FIG. 10. Removingoverlap ensures that pixels are not rasterized more than once, which cancause unnecessary repetition of work for the rasterizer and reduceoverall performance. In addition, errors in pixel exposure dose canoccur: for example, “greater than black” or “greater than white” pixels(due to overwriting). This problem could be solved by clipping to blackor white, but this solution will not be applicable where half-toning isbeing used. In addition to dose errors, overlaps can also lead topattern position errors. In the next stage, the resulting shapes arethen decomposed into individual trapezoids as shown in FIG. 11, whichcan be described and stored as discussed above.

The offline pre-processor 520 can be configured to divide the patterndata into portions corresponding to different slices of the requestedpattern. These portions can be processed independently and forwarded toseparate online preprocessors and online rasterizers. For example, asingle offline pre-processor 520 can be arranged to produce a pluralityof files corresponding to intermediate representations of differentslices of the pattern. The plurality of files can then be forwarded to acorresponding plurality of online rasterizers so as to be rasterized inparallel. Each of the slices can correspond, for example, with a portionof the pattern to be exposed by one of the optical engine spot arraysSA. The above arrangements and/or combinations thereof can allow theoverall online rasterization to be carried out more efficiently (i.e.,using a smaller number of computing operations—for example,multiplication or memory access—and/or more quickly for a given cost ofapparatus).

FIG. 12 shows how a pattern for an entire substrate can be divided,according to one embodiment of the present invention. The substrate W isdepicted relative to a horizontal scanning direction (indicated by arrow1210). The requested pattern comprises six flat panel displays definedby display areas 1220 (comprising display pixels) and border areas 1230(comprising patterns for connecting wires, etc.). The overall pattern isdivided into five slices, delimited by broken lines 1240.

FIG. 13 depicts an offline pre-processor 520 configured to exploit thedifference in content between the display and border areas of patternsfor flat panel displays, according to one embodiment of the presentinvention. In this embodiment, offline pre-processor 520 comprises twocompression devices: a display area compression device 1310 and a borderarea compression device 1320. The display area compression device 1310can operate using a dictionary-based compression algorithm, for example,based on a single dictionary entry for each type of display pixel in thedisplay (normally, only one type of pixel will be used), or othersuitably specialized compression method. The border regions, on theother hand, are likely to be less well-ordered and are dealt with by theborder area compression device 1320 using two-dimensional run-lengthencoding or trapezoid decomposition as discussed above. By applyingcompression algorithms that are better adapted to the input pattern,compression and/or decompression can be achieved more effectively.

As discussed above, the bitmap expansion of the GDSII vectorrepresentation of the mask layout (and therefore device pattern) can beextremely large. When the image contains repetitive patterns, imagecompression can reduce the amount of data considerably, reducing storagedemands and data transport times. However, it has proven difficult todesign a de-compression algorithm that can output the pixel values atthe required rate (for example, 10¹⁰ pixels/sec) for a reasonable costand reliability.

According to one embodiment of the invention, a quadtree representationis adapted for this purpose. In particular, the offline pre-processingdevice 520 is configured to convert the non-bitmap descriptiverepresentation to a quadtree representation, which can be rasterizedonline.

In one example, the quadtree representation comprises a recursive tree,in which the image is divided into four parts at each node. Each of thefour parts can be characterized by the extent to which they are filledby the pattern to be represented. Each part is then split again intofour and the process continues until branch termination conditions areachieved for all branches. For example, a branch can terminate when allof the quadrants under a given node are filled completely, or filledabove a predetermined threshold value. Additionally, a branch willterminate when all four quadrants are empty.

FIG. 14 shows how a pattern 1400 can be divided in order to build up aquadtree representation, according to one embodiment of the presentinvention. The process is shown in five steps: 1401, 1402, 1403, 1404,and 1405. Frame 1401 represents the root node and is undivided. Thefirst division into four quadrants is shown in frame 1402. Each of thefour quadrants are partially filled by portions of the pattern 1400, andare therefore each divided further. In frame 1403, not all of thequadrants are partially filled, the empty ones will be divided nofurther and this fact will be recorded in the file (these are the“leaves of the tree”), while the partially filled quadrants will bedivided further. The next levels of division are shown in frames 1404and 1405. It can be seen that the grid is defined more densely aroundthe pattern 1400, where it is most needed, and less densely elsewhere.This allows efficient representation of the pattern because fewer bytesare required where the grid is less dense.

Software for converting a GDSII file to a quadtree representation iscommercially available so that this functionality of the pre-processor520 can be implemented at low cost. In one example, the decompressionalgorithm involving a recursion means will implemented effectively inhardware (particularly in a massively parallel processing environment)because the recursion will involve a number of identical steps, whichcan be executed on processors allocated from a pool of identicalprocessors. The quadtree method is particularly suitable forrepresenting black and white bitmap patterns. Gray tone pixels could beachieved, for example, by first generating a high resolution black andwhite image and converting blocks of black and white pixels into singlegray tone pixels. For example, a 15 by 15 array of 50 nm pixels can beconverted to a single gray tone pixel of 750 nm square.

In one example, a particularly efficient representation can be obtainedby allowing the quadtree to start in a more flexible manner. Forexample, instead of splitting the pattern into four quadrants for thefirst node, the pattern can be divided into a different number ofregions of variable geometries (this can be termed a “multi-tree”representation because, where subsequent nodes are treated in the normalquadtree representation, it effectively comprises a plurality of normalquadtree representations). In this way, a special quadtreerepresentation can be achieved that is better adapted to the lithographyapparatus. For example, the first division can be arranged to be inunits that reflect the machine geometry. For example, the pattern can besplit into parts that represent the exposure window and strokes of theexposure window that are projected by one of the optical system spotarrays SA as the substrate W is scanned past. More particularly, insystems comprising a plurality of patterning arrays, the pattern can besplit into portions that represent regions exposed by particularpatterning arrays (and/or particular portions of patterning arrays) atparticular times, in such a way that the entire pattern is representedand the data associated with particular areas of the pattern canefficiently be rasterized in the order in which they are required.

FIG. 15 shows an arrangement, according to one embodiment of the dpresent invention. The pattern is divided into a number of parallelstrips 1501, 1502, 1503, 1504 and 1505, which allow the image processingto be split between different optical systems and different parts of thedata-path architecture. An exposure window, which represents a region ofthe pattern that is exposed during a particular period is shown byrectangle 1520 and the substrate W is arranged to move relative to theprojection optics in the sense indicated by arrow 1510. The multi-treeroot nodes are illustrated for strip 1504 as regions 1540. The region1540 overlapping at the instance shown in the diagram with the exposurewindow has been expanded to illustrate how the pattern contained thereincan be dealt with by a quadtree representation for all nodes below thatmulti-tree root node.

According to this embodiment, the decompression can then be carried outin parallel for each optical engine (because the first node is limitedto be entirely within the region of the pattern dealt with by oneengine). Alternatively or additionally, in the case where the bitmapsresulting from expansion of each of the regions 1540 in a given sliceare needed at different times, individual decompression of the patternwithin the corresponding regions can be carried out in an appropriatesequence. Because the pattern has been split up as part of theconversion process to the quadtree representation, there is no longerany need to decompress the whole pattern in one operation. Selectedportions can be decompressed at selected times according to the needs ofthe lithography apparatus.

Although specific reference can be made in this text to the use oflithographic apparatus in the manufacture of a specific device (e.g., anintegrated circuit or a flat panel display), it should be understoodthat the lithographic apparatus described herein can have otherapplications. Applications include, but are not limited to, themanufacture of integrated circuits, integrated optical systems, guidanceand detection patterns for magnetic domain memories, flat-paneldisplays, liquid-crystal displays (LCDs), thin-film magnetic heads,micro-electromechanical devices (MEMS), etc. Also, for instance in aflat panel display, the present apparatus can be used to assist in thecreation of a variety of layers, e.g., a thin film transistor layerand/or a color filter layer. imprint lithography, where the contextallows, and is not limited to optical lithography. In imprintlithography a topography in a patterning device defines the patterncreated on a substrate. The topography of the patterning device can bepressed into a layer of resist supplied to the substrate whereupon theresist is cured by applying electromagnetic radiation, heat, pressure ora combination thereof. The patterning device is moved out of the resistleaving a pattern in it after the resist is cured.

While specific embodiments of the invention have been described above,it will be appreciated that the invention can be practiced otherwisethan as described. For example, the invention can take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g., semiconductor memory, magnetic or optical disk) havingsuch a computer program stored therein.

CONCLUSION

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be apparent to persons skilledin the relevant art that various changes in form and detail can be madetherein without departing from the spirit and scope of the invention.Thus, the breadth and scope of the present invention should not belimited by any of the above-described exemplary embodiments, but shouldbe defined only in accordance with the following claims and theirequivalents.

It is to be appreciated that the Detailed Description section, and notthe Summary and Abstract sections, is intended to be used to interpretthe claims. The Summary and Abstract sections may set forth one or more,but not all exemplary embodiments of the present invention ascontemplated by the inventor(s), and thus, are not intended to limit thepresent invention and the appended claims in any way.

1. A lithographic apparatus, comprising: an array of individuallycontrollable elements that modulate a beam of radiation; a dataprocessing pipeline that converts a first representation of a requesteddose pattern to a sequence of control data suitable for controlling thearray of individually controllable elements to substantially form therequested dose pattern on a substrate, wherein the data processingpipeline comprises: an offline pre-processing device that converts thefirst representation of the requested dose pattern to an intermediaterepresentation that is rasterized in a fewer number of operations thanthe first representation; a storage device that stores the intermediaterepresentation; and an online rasterizer that accesses the storedintermediate representation and produces therefrom a stream of bitmapdata to be used to generate the sequence of control data substantiallyin real time.
 2. The lithographic apparatus according to claim 1,wherein the intermediate representation is rasterized in a fewer numberof memory access operations than the first representation.
 3. Thelithographic apparatus according to claim 1, wherein the intermediaterepresentation is rasterized using less computational hardware than thefirst representation.
 4. The lithographic apparatus according to claim1, wherein the first representation represents repeating groups ofelements in the requested dose pattern using a hierarchy.
 5. Thelithographic apparatus according to claim 4, wherein the intermediaterepresentation contains at least one level of hierarchy less than thefirst representation from which it is derived.
 6. The lithographicapparatus according to claim 5, wherein the intermediate representationhas only a single level of hierarchy.
 7. The lithographic apparatusaccording to claim 6, wherein the requested dose pattern corresponds toa device layer in the manufacture of Flat Panel Displays and the singlelevel of hierarchy represents a plurality of identical Flat PanelDisplay pixels.
 8. The lithographic apparatus according to claim 1,wherein the offline preprocessing device divides requested dose patterndata in the first representation into a plurality of portions, eachcorresponding to a particular region of the requested dose pattern, andwherein each portion is converted to an intermediate representation andrasterized separately.
 9. The lithographic apparatus according to claim1, wherein the first representation expresses the requested dose patternin terms of overlapping geometric units and the preprocessing deviceproduces an intermediate representation in which the overlap is at leastpartially removed.
 10. The lithographic apparatus according to claim 1,wherein: each portion of the requested pattern represented by a vectorin the first representation is represented in the intermediaterepresentation by the X and Y coordinates of a first point of the vectorto be exposed, an angle of the vector relative to an axis lying in aplane of the substrate, and the Y-coordinate or X-coordinate of a lastpoint of the vector to be exposed; the X and Y axes are orthogonal axeslying in the plane of the substrate; and the Y-axis is substantiallyparallel to a scanning direction of the substrate relative to the arrayof individually controllable elements.
 11. The lithographic apparatusaccording to claim 1, wherein: portions of the requested patternrepresented by curves in the first representation are each representedin the intermediate representation by the X and Y coordinates of a firstpoint of a curved portion to be exposed, a mathematical relationdescribing a shape of the curved portion, and the Y-coordinate orX-coordinate of a last point of the curved portion to be exposed; andthe X and Y axes are orthogonal axes lying in the plane of the substrateand the Y-axis is substantially parallel to a scanning direction of thesubstrate relative to the array of individually controllable elements.12. The lithographic apparatus according to claim 1, wherein: the bitmapdata is composed of a sequence of lines of bitmap values, orderedsubstantially according to an exposure sequence of portions of therequested pattern defined by the lines; a plurality of modificationrules define how the bitmap values change from line to line in thesequence of lines; each one of at least a subset of the modificationrules is derivable from a corresponding portion of the requested dosepattern represented by a vector and is applicable for all lines affectedby that vector; and the offline pre-processing device produces anintermediate representation comprising a sequence of data packets, eachdescribing how a group of modification rules relevant for a given lineis different from a group of modification rules relevant for a precedingline.
 13. The lithographic apparatus according to claim 12, wherein: thebitmap data uses a 1-dimensional run-length encoding to represent eachline of bitmap values; and the modification rules define how the1-dimensional run-length encoding of each line of bitmap values changesfrom line to line in the sequence of lines.
 14. The lithographicapparatus according to claim 1, wherein: the bitmap data is composed ofa sequence of lines of bitmap values, ordered substantially according toan exposure sequence of portions of the requested pattern defined by thelines; a plurality of modification rules define how the bitmap valueschange from line to line in the sequence of lines; each one of at leasta subset of the modification rules is derivable from a correspondingportion of the requested dose pattern represented by a curved sectionwith constant properties and is applicable for all lines affected bythat curved section; and the offline pre-processing device produces anintermediate representation comprising a sequence of data packets, eachdescribing how a group of modification rules relevant for a given lineis different from a group of modification rules relevant for a precedingline.
 15. The lithographic apparatus according to claim 14, wherein: thebitmap data uses a 1-dimensional run-length encoding to represent eachthe line of bitmap values; and the modification rules define how the1-dimensional run-length encoding of each line of bitmap values changesfrom line to line in the sequence of lines.
 16. The lithographicapparatus according to claim 1, wherein portions of the requestedpattern represented by vectors in the first representation arere-ordered by the offline pre-processing device and stored in theintermediate representation in such a way as to be accessible to theonline rasterizer substantially in the order in which each vectorcontributes to the sequence of control data.
 17. The lithographicapparatus according to claim 1, wherein portions of the requestedpattern represented by curves in the first representation are re-orderedby the offline pre-processing device and stored in the intermediaterepresentation in such a way as to be accessible to the onlinerasterizer substantially in the order in which each curved portioncontributes to the sequence of control data.
 18. The lithographicapparatus according to claim 1, wherein features of the firstrepresentation are described in the intermediate representation in termsof a plurality of non-overlapping polygons.
 19. The lithographicapparatus according to claim 18, wherein the polygons are ordered by theoffline pre-processing device and stored in the intermediaterepresentation in such a way as to be accessible to the onlinerasterizer substantially in the order in which each polygon contributesto the sequence of control data.
 20. The lithographic apparatusaccording to claim 18, wherein the non-overlapping polygons aretrapezoids.
 21. The lithographic apparatus according to claim 1, whereinthe storage device is accessible by the online rasterizer and configuredto store at least the portion of the intermediate representation of therequested dose pattern relevant to the portion of the pattern beingrasterized at any given time.
 22. The lithographic apparatus accordingto claim 5, further comprising: an online pre-processing deviceconfigured to remove all remaining levels of hierarchy in theintermediate representation and pass the resulting flattenedintermediate representation to the online rasterizer.
 23. Thelithographic apparatus according to claim 1, wherein the intermediaterepresentation comprises a quadtree representation of the requested dosepattern.
 24. The lithographic apparatus according to claim 23, furthercomprising a plurality of the arrays of individually controllableelements, wherein the intermediate representation comprises amulti-quadtree representation in which the root node for each treesubstantially corresponds to a region of the substrate exposed by one ofthe plurality of arrays of individually controllable elements at aparticular time.
 25. A device manufacturing method, comprising:modulating a beam of radiation using an array of individuallycontrollable elements; converting a first representation of a requesteddose pattern to a sequence of control data suitable for controlling thearray of individually controllable elements in order substantially toform the requested dose pattern on a substrate; converting the firstrepresentation of the requested dose pattern offline to an intermediaterepresentation that is rasterized in a fewer number of operations thanthe first representation; storing the intermediate representation in astorage device; and accessing the stored intermediate representation andproducing therefrom a stream of bitmap data to be used to generate thesequence of control data substantially in real time.
 26. The devicemanufacturing method according to claim 25, wherein: the bitmap data iscomposed of a sequence of lines of bitmap values, ordered substantiallyaccording to an exposure sequence of portions of the requested patterndefined by the lines; and a plurality of modification rules define howthe bitmap values change from line to line in the sequence of lines, theplurality of modification rules comprising, deriving each one of atleast a subset of the modification rules from a corresponding portion ofthe requested dose pattern represented by a vector and applying eachsuch modification rule for all lines affected by the correspondingvector; and producing an intermediate representation comprising asequence of data packets, each describing how a group of modificationrules relevant for a given line is different from a group ofmodification rules relevant for a preceding line.
 27. The devicemanufacturing method according to claim 26, wherein the bitmap data usesa 1-dimensional run-length encoding to represent each the line of bitmapvalues and the modification rules define how the 1-dimensionalrun-length encoding of each line of bitmap values changes from line toline in the sequence of lines.
 28. The device manufacturing methodaccording to claim 25, wherein: the bitmap data is composed of asequence of lines of bitmap values, ordered substantially according toan exposure sequence of portions of the requested pattern defined by thelines; and a plurality of modification rules define how the bitmapvalues change from line to line in the sequence of lines, the pluralityof modification rules comprising, deriving each one of at least a subsetof the modification rules from a corresponding portion of the requesteddose pattern represented by a curved section with constant propertiesand applying each such modification rule for all lines affected by thatcurved section; and producing an intermediate representation comprisinga sequence of data packets, each describing how a group of modificationrules relevant for a given line is different from a group ofmodification rules relevant for a preceding line.
 29. The devicemanufacturing method according to claim 28, wherein the bitmap data usesa 1-dimensional run-length encoding to represent each the line of bitmapvalues and the modification rules define how the 1-dimensionalrun-length encoding of each line of bitmap values changes from line toline in the sequence of lines.
 30. A flat-panel display manufacturedaccording to the method of claim
 25. 31. An integrated circuit devicemanufactured according to the method of claim
 25. 32. A computerreadable medium having a computer program for controlling a lithographicapparatus having a computer program logic recorded thereon forcontrolling at least one processor, the computer program logiccomprising: computer program code means for modulating a beam ofradiation using an array of individually controllable elements; computerprogram code means for converting a first representation of a requesteddose pattern to a sequence of control data suitable for controlling thearray of individually controllable elements in order substantially toform the requested dose pattern on a substrate; computer program codemeans for converting the first representation of the requested dosepattern offline to an intermediate representation that is rasterized ina fewer number of operations than the first representation; computerprogram code means for storing the intermediate representation in astorage device; and computer program code means for accessing the storedintermediate representation and producing therefrom a stream of bitmapdata to be used to generate the sequence of control data substantiallyin real time.